一个 SQL 查询，用于显示当月的最后一个营业日

Question

Here is my query:

CREATE FUNCTION dbo.ufn_LastBusinessDayOfMonth (@Dt datetime)
RETURNS datetime
AS
BEGIN
  DECLARE @dt2 datetime
  DECLARE @Df int
  DECLARE @dSat int
  DECLARE @dSun int
  SELECT
    @dt2 = DATEADD(D, -1, DATEADD(m, 1 + DATEDIFF(m, 0, @Dt), 0))
  SELECT
    @dSat = DATEPART(dw, '2018-01-06') -- Known Saturday
  SELECT
    @dSun = (@dSat % 7) + 1

  SELECT
    @dt2 = (
    CASE
      WHEN DATEPART(dw, @dt2) = @dSun THEN DATEADD(DAY, -2, @dt2)
      WHEN DATEPART(dw, @dt2) = @dSat THEN DATEADD(DAY, -1, @dt2)
      ELSE @dt2
    END)

  RETURN @dt2
END

Answer 1

DECLARE @Dt datetime
SET @Dt = '03/21/2018'

DECLARE @lastOfMonth datetime, @3DaysBeforeTheEnd DATETIME

set @lastOfMonth = DATEADD(s,-1,DATEADD(mm, DATEDIFF(m,0,@Dt)+1,0))
SET @3DaysBeforeTheEnd = DATEADD(d,-2,@lastOfMonth)



select top 1 DATENAME(weekday, x.[Date]), x.[Date]
from (
SELECT  TOP (DATEDIFF(DAY, @3DaysBeforeTheEnd, @lastOfMonth) + 1)
        [Date] = DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY a.object_id) - 1, @3DaysBeforeTheEnd)
FROM    sys.all_objects a
        CROSS JOIN sys.all_objects b
        )x
WHERE DATENAME(weekday, x.[Date]) NOT IN ('Saturday','sunday')
order by x.[Date] desc